The vascular smooth muscle cell (SMC) alters its molecular and phenotypic characteristics during pathological vascular remodeling. Both Notch and TGF signaling pathways promote a differentiated, contractile phenotype characteristic of mature SMC. However, mechanisms by which these pathways interact with each other are only beginning to be understood. Mutations in either pathway are causal for human cardiovascular disease, and therapies targeting these pathways are currently in clinical trials. Our laboratory discovered a regulatory interaction between Notch and Smad in SMC, which links Notch and TGF/BMP/Smad signaling. Concomitant Notch and TGF signaling leads to synergistic activation of phosphoSmad (pSmad) transcriptional activity and SMC marker expression. The goal of this project is to define mechanisms of integrative molecular signaling leading to SMC differentiation. This project utilizes molecular and biochemical signaling approaches in human primary vascular cells, and mouse transgenic models to study in vivo gene regulation and function. We propose the following hypotheses: 1) Jagged1 activation of Notch signaling in SMC transcriptionally represses the TGF co-receptor, endoglin, via the canonical CBF-1 mediated pathway. 2) Coordinate Notch and TGF signaling leads to synergistic activation of SMC contractile genes via interaction of CBF1- and pSmad- containing transcriptional complexes. 3) Activation of Notch in vivo in SMC prior to vascular injury will maintain the differentiated phenotype, leading to suppressed neointimal lesion formation and arteriogenesis. Specific Aim 1: Test the hypothesis that the TGF co-receptor, endoglin, is transcriptionally regulated by Notch signaling in SMC. This aim will utilize molecular assays in vitro and transgenic mouse models in vivo to characterize Notch regulation of endoglin expression and TGF signaling in SMC. Specific Aim 2: Characterize the interaction of CBF1 and Smad transcriptional complexes on SMC contractile genes. We hypothesize that CBF1 and pSmad transcriptional complexes interact to transcriptionally regulate contractile genes including smooth muscle -actin (SM actin) and calponin1. Specific Aim 3: Determine how the regulation of endoglin and TGF signaling by Notch affects pathological vascular remodeling. Established mouse transgenic strains will be evaluated in vascular disease models.